He worked in a variety of media including oil, tempera, gouache, watercolour and pastel. Tunnard's first major exhibition, held in 1932 at the Redfern Gallery, featured landscapes, marine scenes and still life.

From the mid-1930s, however, he began to paint abstract works influenced by the styles of Joan Miró and Paul Klee, and further embraced British surrealism on reading Herbert Read's Surrealism. Tunnard had a solo exhibition at the Guggenheim Jeune gallery in 1938.

In her autobiography, Peggy Guggenheim described his colour as exquisite :I was happy to think that I had discovered a genius." Tunnard's compositions, with their Neo-Romantic sensibility, are often compared to that of Graham Sutherland.

In later life he became interested in space travel depicting satellites and moonscapes in his paintings.